The present invention relates to cutting elements of the type which are mounted on rotary drill bits for cutting through earth formations (including rock formations), cement, plugs, etc.
Rotary drilling operations in earth formations are typically carried out using a rotary drill bit which is simultaneously rotated and advanced into the formation. Cutting is performed by cutting elements mounted on the drill bit, and the cuttings are flushed to the top of the borehole by the circulation of drilling fluid.
A conventional cutting element may comprise a cutting blank mounted on a cemented carbide stud. The blank may include a diamond disk disposed on a carbide substrate. The blank can be braze bonded to an inclined face of the stud, and the stud 18 is then secured, e.g., by press-fit, in a recess of the drill bit. Cutting elements of this type are disclosed, for example, in Rowley et al U.S. Pat. No. 4,073,354; Rohde et al U.S. Pat. No. 4,098,363; and Daniels et al U.S. Pat. No. 4,156,329. During the use of cutting elements of this type, cutting takes place by means of a section of the peripheral edge of the blank which is brought into contact with the formation being cut. While being effective in relatively soft formations, such a cutter is much less effective in hard formations (e.g., rock), due to the relatively large portion of the diamond layer which contacts the formation. Also, a large cutting portion results in the occurrence of considerable friction-generated heat which accelerates the deterioration of the cutting element.
Cutter element configurations have been proposed in Dennis et al U.S. Pat. No. 4,255,165 issued Mar. 10, 1981 in which a claw-like cutting action is to be achieved by "fingers" of diamond material formed by means of a technique which involves the sandwiching of a diamond mix between carbon layers and the application of high temperature and high pressure. However, serious problems were encountered when attempts were made to reduce such cutters to practice. Possibly, a major contributing factor to those problems related to the sandwiching of the diamond layer between the carbide layers whereby the "cobalt sweep" from the cemented carbide through the diamond (resulting from the melting of the cobalt by the high temperatures) occurred in such manner that impurities were swept to, and accumulated at, an internal region of the diamond layer along with excess cobalt. Impurities and excess cobalt which accumulate in that manner tend to cause the diamond layer to separate and create a weakened, poorly sintered zone which is particularly susceptible to cracking during a cutting operation. It would be desirable, then, to provide a cutting element which exhibits a claw-like cutting action and yet which is durable and firmly reinforced.
It would also be desirable to provide a cutting element wherein the diamond layer is more securely adhered to a substrate than in conventional cases wherein a diamond disk is adhered to a substrate.
It is, therefore, an object of the present invention to provide a cutting element which exhibits a claw-like or finger-like cutting action and yet which is highly durable and firmly reinforced.
A further object is to provide such a cutting element which can be produced under high or low temperature conditions.
An additional object is to produce a cutting element wherein, when produced under high temperature conditions, the resulting "cobalt sweep" causes at least most impurities and excess cobalt to be swept out of the interior of the diamond layer.
An additional object is to provide such a cutting element with diamond cutting strips which are firmly reinforced along three sides.
A further object is to provide such a cutting element which minimizes the amount of friction generated during use.
One further object is to provide such a cutting element which minimizes cost by significantly reducing the amount of diamond in the cutting element.